Soap based cleansing composition provides antibacterial benefits largely associated with the removal of organisms from a surface through the cleansing/detergency action of such products. Such compositions commonly have biocidal action against many gram negative bacteria. The biocidal action of soap compositions against gram positive bacteria is considerably more limited within the contact times typical of product use, generally under 1 minute, and more commonly of the order of 30 seconds or less. Achieving biocidal action against gram positive bacteria is especially problematic in the case of high pH cleansing compositions, by which is meant that a 1 wt % solution thereof in water has a pH in a range of from 9 to 12 at 25° C.
Various routes to improving the biocidal activity of soap based cleansing compositions have been suggested.
US2008014247A (Lu et al., 2008) discloses a composition having metal containing material, stearic acid and a pharmaceutically acceptable carrier to treat conditions caused by gram-positive, gram-negative, fungal pathogens and/or antibiotic-resistant bacteria. It further provides a method for inhibiting biofilm proliferation. The metal containing material can be silver.
U.S. Pat. No. 3,050,467 B1 (Horowitz et al. 1962) discloses an antimicrobial cleansing composition consisting essentially of a mixture of a water-soluble soap and a silver salt of partially depolymerized alginic acid. The composition provides synergestic antimicrobial activity.
US2011224120 AA (Henkel) discloses liquid washing compositions having surfactant, silver and/or a silver compound and a non-neutralized fatty acid.
Our copending application EP14152965 (Unilever, 2014) discloses an alkaline cleansing composition of pH at least 9 having anionic surfactant including soap, silver and 0.01 to 10 wt % fatty acids providing a robust cleaning composition.
When silver compound is used in soap based cleaning compositions, silver at levels providing antimicrobial benefits as suggested in prior art is relatively unstable, undergoes discoloration and is aesthetically unpleasant.
Prior disclosures have not addressed the issue of providing an antimicrobial cleansing composition that affords an effective, fast, and broad spectrum control of bacteria and exhibits acceptable aesthetic properties.
Thus an object of the present invention is to provide an antimicrobial cleansing composition that provides biocidal activity in relatively short contact times of 1 minute to 10 seconds.
Another object of the present invention is to provide an antimicrobial cleansing composition which provides antimicrobial activity at very low concentration of silver compound.
A further object of the present invention is to provide an antimicrobial cleansing composition which has consumer-acceptable aesthetic properties.
A still further object of the present invention is to provide an antimicrobial composition that is highly efficacious against a broad spectrum of gram positive and gram negative bacteria.
We have determined that antibacterial activity in relatively short contact times against gram positive and gram negative microorganisms in a soap based cleansing composition having silver compound enhances considerably in presence of a further salt of carboxylic acid. It has been additionally found that the antibacterial activity is enhanced even at very low concentrations of silver compound.
Given the relatively high cost of silver, such low levels of silver compound provides for significant cost benefits, compared to the higher levels of silver compounds required to provide significant biocidal effect within the contact times of interest. Additionally, the low levels of silver compound are desirable from both a sensory and process vantage.